High Sensitivity and Fast Oxidation of Caffeine in Coffee and Theophylline at Nanostructured Electrodes

Significantly higher than previously reported sensitivity was achieved in the electrochemical determinations of caffeine (CA) and theophylline (TP) at a nanostructured carbon fiber electrode (CFE) sensor by fast scan voltammetry (FSV), where apparent catalysis of the oxidation was observed. For CA the oxidation was reversible and the oxidation potential in aqueous solutions was similar to the potentials reported from cyclic voltammetry (CV) in aprotic solvents, indicating similar oxidation pathways, forming CA radicals. For TP, the reversible oxidation potential was higher, in agreement with TP structure. Formal potentials in aqueous solutions that have been previously unavailable from electrochemistry of CA and TP were thus obtained. In the determinations of CA and TP, sensitivity and linear dynamic range (LDR) in FSV were 1.84 mAcm(-2) mM(-1) and 0.20-22.0 mmolL(-1) and 1.46 mAcm(-2) mM(-1) and 0.50-30.0 mmolL(-1), respectively. FSV determination of CA in coffee sample is demonstrated and the results are in agreement with the results obtained by HPLC-UV.